The invention relates to an apparatus for forming a cloud of magnetic toner particles and, more particularly, improvement of an apparatus for forming a cloud of one-component type developer, or magnetic toner particles in an apparatus for developing electrostatic latent image or an apparatus for selectively separating toner particles into magnetic and non-magnetic toner particles.
There have been various types of apparatus for supplying toner particles onto a photoelectroconductive layer surface with an electrostatic charged image formed thereon, for example, U.S. Pat. Nos. 3,645,770, 3,707,389, 3,882,822 and 3,962,992. U.S. Pat. No. 3,962,992, discloses the principle for forming a layer of cloud of toner particles by rotating and repeatedly rebounding toner particles in the alternating magnetic field. The developing apparatus using the alternating magnetic field employs a one-component type developer, or magnetic toner particles each of which is made of magnetic particle covered with resin colored by an agent. Such a developing apparatus will be described in more detail referring to FIG. 1. As shown in FIG. 1, the developing apparatus is comprised of a hopper 4 for supplying magnetic toner or developer 2, and a cylindrical non-magnetic sleeve 6 supplied with magnetic toner particles 2 from the hopper 4, and a magnet roller 8 disposed within the sleeve 6. The magnet roller 8 is provided with a number of magnetic poles N and S alternately arranged on the roller surface. The magnet roller 8 is rotated in a direction of an arrow 10 or the cylindrical sleeve 6 is rotated in a reverse direction with respect to arrow 10, for forming an alternating magnetic field on the sleeve surface. The magnetic toner particles 2 supplied from the hopper 4 fall onto the sleeve surface due to the forces of gravity and of the magnetic force. The toner particles on the sleeve surface are carried with the rotation of the roller 8 or the sleeve 6. The thickness or height of the carrying particles 2 from the sleeve surface are uniformly controlled by a doctor blade 12 which is disposed above the sleeve surface and upstream of the hopper 4. The toner particles 2 are carried to contact with a photoconductive layer 14 of a rotating drum 16 or a photoconductive paper (not shown) so that the toner particles 2 are attached onto the surface of the layer 14 to visualize electrostatic latent images already formed thereon.
In this type of developing apparatus, it is difficult to always keep constant an amount of carrying magnetic toner particles 2 with a proper particle density on the sleeve surface. The result is that the cloud of particles are not uniformly contacted with the photoconductive layer 14. This uneveness is distinguished, particularly when the toner particles are poor in fluidity and when an aggregation or conglomerate of particles are included in the magnetic toner particles since the amount of the carrying particles is not uniform.